This invention relates to technique for inspecting a semiconductor device; and, more particularly, the invention relates to a wafer inspection method and apparatus suitable for control of defective conditions which occur in the fabricating processes carried out in a semiconductor device production line.
In a semiconductor device, a conduction failure of contact holes leads to fatal defects, including characteristic failures, and has a significant impact on the yield of the semiconductor device. Such a failure is often caused by changes in production requirements or defective operation of manufacturing equipment and often results in the production of a large amount of defective units. Such defective conditions in process are controlled, in general, by periodically checking for changes in pattern geometries with a critical dimension measurement SEM. However, the evaluation of pattern geometries alone cannot directly identify the conducting state of contact parts.
On the other hand, JP-A No. 2000-58608 discloses a method of detecting conduction failures by using the brightness of contact parts as well as pattern geometries. This method utilizes a feature of an electron microscope image. The charge-up amount of a pattern produced by irradiation of electron beams thereon varies depending on the conducting states of contact parts and shows a contrast between normal parts and defective parts on a secondary electron image to be detected. With such a method, it is possible to inspect electrical characteristics that cannot be checked by a visual check of the external view.
In recent years, a wafer inspection apparatus using SEM images has also come to be utilized, as disclosed in JP-A Nos. 1993-258703 and 2000-208085, and efficient defect inspection has became possible. This kind of apparatus utilizes the repeatability of the same patterns containing devices such as cells and chips within the conductor traces and compares images of these patterns to detect defects.
As stated above, a method using SEM images has come into widespread usage as a means of detecting electrical conduction failures of contact windows. However, this method requires a considerably long tine to obtain an SEM image with a high signal-to-noise ratio and high resolution; in this regard, it takes a few hours to tens of hours to perform inspection of a whole wafer. Therefore, the in-line usage of this method is difficult. In addition, an inspection method involving comparison of images has a drawback in that, when there is a quantity occurrence of defects, images of the defects are compared with each other, making an accurate defect inspection difficult.
In addition, all of these inspection methods are intended for defect inspection, so they cannot predict the occurrence of electrical conduction failures. However, since failures caused by changes in production requirements and defective conditions of manufacturing equipment can suddenly be encountered in a large amount and on a massive scale and invite too many wafers with defects at the time of the occurrence, it is desirable to detect changes in processes.